1. Field of the Invention
This invention relates to a foldable and extensible structure and, more particularly, to a foldable and curvilinearly extensible structure and method, the structure fabricated from a plurality of base modules, each base module being configurated from six rigid members flexibly interconnected end-to-end by swivels in a closed configuration generally approximating a double isosceles triangle in appearance when folded flat and having intersecting rigid members pivotally secured with the location of one pivot at the midpoint of the base of the isosceles triangle as defined by the respective rigid members and the other two pivots offset from the swivels adjacent the base by a distance equal to one-half the base to thereby impart a desired external contour to the curvilinear configuration and to provide the desired folding and unfolding characteristics.
2. The Prior Art
Extensible structures are well-known in the art and one particularly familiar form of an extensible arm structure is the common "scissors" extension arm. The scissors extension arm involves at least a first pair of pivotally joined rigid members. The structure may also include additional pairs of rigid members adjoined to the ends of the first pair in an end-to-end relationship. Lateral movement of the free ends of the rigid members imparts a corresponding movement to the pivotally interconnected pairs of rigid members resulting in a linear contraction and/or extension of the scissors extension arm. While this well-known apparatus is found in numerous applications, it is generally considered to be a two-dimensional configuration and therefore lacks the necessary structural stability for various applications. Additionally, the nature of the construction limits the extension of the scissors extension arm to a generally straight line.
The foregoing limitations of a two-dimensional structure have been overcome by the apparatus disclosed in my previous patent, U.S. Pat. No. 4,155,975, issued Sept. 26, 1978. In this patent, the basic element of the foldable and extensible structure is a foldable and extensible base module. The base module is fabricated from six equal-length, rigid members swivelly interconnected end-to-end in a closed figure with intersecting rigid members being pivotally connected adjacent the midpoint of the rigid members. A plurality of the base modules are selectively interconnected at adjacent swivels and may include additional rigid struts to thereby provide an enlarged, foldable and extensible truss-like structure. However, in each of the configurations set forth in this patent, extension is limited to a straight line or plane and is, therefore, incapable of being extended in a curvilinear configuration.
Zeigler (U.S. Pat. No. 3,968,808) discloses a collapsible, self-supporting structure made up of a network of rod elements pivotally joined at their ends and forming scissor-like pairs in which rod element crossing points are pivotally joined.
Zeigler (U.S. Pat. No. 4,026,313) discloses a collapsible, self-supporting structure in which basic assemblies of crossed rod elements are employed to achieve the desired shape. Further, the crossing points of crossed rod element in the structure may include limited sliding connections to affect the transfer of collapsing force to other crossing points which are pivotally joined.
Lotto, et al (U.S. Pat. No. 4,017,932) discloses a temporary, modular, self-erecting bridge which is expandable to form a truss-like structure.
While the foregoing list of references have come to the attention of the inventor, no representation is made that all of these references may be "prior art" within the meaning of that term under the provisions of 35 USC 102 or 35 USC 103, although these references are disclosed herein so as to fully comply with the duty of candor and good faith as required in 37 CFR 1.56.
In view of the foregoing, it would be an advancement in the art to provide a foldable and extensible structure which is extensible in a generally curvilinear orientation, the curvature of the curvilinear configuration being a function of the length of the rigid members with a corresponding placement of the pivotal points on the structure, and the degree of extension of the structure. It would also be an advancement in the art to provide a novel foldable and curvilinearly extensible structure wherein the rigid members are configurated with a predetermined arcuate curve therein to thereby provide a predetermined toroidal profile to the structure.